Many structural systems are designed to resist deformation and damage by exhibiting high stiffness. High stiffness may allow a system to withstand applied forces without large amounts of associated movement by the system. However, high stiffness may also create a system having an increased risk of catastrophic failure when a threshold force is exceeded. Therefore, some structural systems are designed to have elasto-plastic deformation characteristics. For example, a system may exhibit substantially elastic deformation characteristics within a first range of applied forces. The removal of forces within that range can result in the system returning to an original state without significant changes to the system (i.e., without permanent deformation or damage). Forces applied in a second range that exceeds the first range (i.e., greater than a threshold force) may cause permanent, plastic deformation of the system. The plastic deformation regime may allow the system to dissipate significant amounts of energy without having to be excessively strong to resist a large force.
The elasto-plastic deformation may be thought of as a curve, such as that depicted in FIG. 1. FIG. 1 shows a graph 100 illustrating a relationship between the amount of force 102 applied and the amount of deformation 104 experienced by a structural system. The first range 106 of applied forces is shown having a substantially linear relationship with deformation. The second range 108 of applied force reflects a substantially linear relationship with deformation, but at a significantly reduced slope, and in some cases, an average slope of zero. The second range 108 depicts a plastic or ductile deformation regime in which the force applied deforms the system inelastically and the system dissipates energy.
While elasto-plastic structural systems have resulted in safer buildings and/or structures, they suffer from a number of drawbacks. For instance, damage to a structural system wrought by both excessive deformation and high accelerations result in repair costs that are very high given the cost of the structural system. Another problem in the design of such systems is the expense of designing a new structural system and/or retrofitting an existing structural system to reflect the desired deformation regimes. Conventional systems may require changes to the sizes of structural members of the system, changes to the type of connection between the structural members, changes to the distribution of structural members, or combinations thereof.